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This expression uses a BackReference to find occurrences of the same word twice in a row (separated by a space). Matches things like 'mandate dated', which may not be desirable. See Sean Carley's update for a better expression for true repeated word matching.

I built this expression to test a string in ASP for valid username and password constraints. It can be adapted for any number of scenerios. For instance in this case, we needed to ensure the username someone wanted was not all numbers or all letters and was 6-15 characters in length with no special characters. This expression tests negatively for all number cases, then all letter cases, and lastly tests for only alphanumeric characters in the required range. In other words: the match must be alphanumeric with at least one number, one letter, and be between 6-15 character in length.

Matches any single upper- or lower-case letter.

Validate against any diner's club card. All diner club cards start with 30,36, or 38, followed by 12 other numbers.

This just a minor mod to Steven Smith's credit card re to accept spaces as separators, as well as return the four parts of the card. [Updated Oct-18-2002 to work with Diners Club/Carte Blanche (prefix must be 36, 38, or 300-305)]

This regex can be used to restrict passwords to a length of 8 to 20 aplhanumeric characters and select special characters. The password also can not start with a digit, underscore or special character and must contain at least one digit.

This pattern returns as much of the first x characters of a string as full words or sentences as a match, where x is currently 20. Change x to adjust the length supported in your database field. I'm currently using this within a string shortening utility to shrink large text regions to word/sentance-boundary elements and appending an ellipsis as a text continuator.

Tests Vehicle Identification Numbers (VINs). This works for a Mitsubishi cars in the UK - but I have been unable to determine whether the format is for UK vehicles or applies only to this make. The requirements are that the first 9 characters and the 11th character are alpha-numeric excluding i, I, o or O. The 10th character is the chassis year, and is alpha-numeric excluding i, I, o, O, q, Q, u, and U. The final 6 characters are numeric. The string is 17 characters in length. Any refinements would be greatly appreciated!

Matches up to three alphabet words separated by spaces with first alphabet character of each word uppercase. Also matches empty strings.

Used to validate Credit Card numbers, Checks if it contains 16 numbers in groups of 4 separated by -, ,or nothing

A regex that attempts to accurately parse the elements from a proper name where the format is in <<First, Last>> order or some permutation of that order. Critiques and suggestions for improvement are welcome.

Incorporated other people's examples; removed extraneous parenthesis on 10/7/04. Currently the SSA site says 772 is the highest AREA number generated (http://www.ssa.gov/employer/highgroup.txt). Old expression was: (^|\s)\d{3}(-?|[\. ])\d{2}\2\d{4}($|\s|[;:,!\.\?]). Looks for either the beginning of a line or whitespace before the beginning of the social security number, then either zero or one hyphen OR one of a period or space, then uses the \3 to reference the value returned in the parenthesis that includes the -?|[\. ] (basically says if the first dash, period, or space is there, then the second one is required; and if the first dash, period, or space is not there, then the second one can't be either), and finally looks for the end of a line, whitespace, or punctuation characters after the social security number.

The "hello world" of regular expressions, this will match any string with an instance of 'foo' in it.

it will check for alphanumeric (Alpha Numeric) values.

Matchs comma delimited numbers. Easily changed to allow for other delimiters. (Edit ",") Does not allow a leading 0 Does not allow groups of numbers with less than 3 numbers, exculding the first group.

This Blacklist RegEx is designed to search a user input for any malicious code or SQL injection attempts.

This regex validates U.S. social security numbers, within the range of numbers that have been currently allocated.

Specifier Format of Guid Values that this RegEx supports: 32 digits: [xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx] 32 digits separated by hyphens: [xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx] 32 digits separated by hyphens, enclosed in brackets: [{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}] 32 digits separated by hyphens, enclosed in parentheses: [(xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)]

Spam trap Catches many and many way to write viagra (replacing letters with similar chars, spacing chars with one space, etc).

This regular expression can be used to parse a comma delimited string. Leading whitespaces (at the beginning of the entire string) and ending commas are not acceptable. Any combination of letters and numbers with zero or one white space between them are acceptable. Note: To change the delimiter, simply replace the comma in the square brackets to the delimiter of choice.